The present invention relates to an acoustic transducer and, in particular, to a miniature flexural piezoelectric transducer for receiving acoustic energy transmitted from a remote source and converting such energy into electrical power for activating an electronic circuit. Further, the present invention relates to a miniature flexural piezoelectric transmitter for transmitting acoustic information by modulating the reflection of an external impinging acoustic wave.
The prior art provides various examples of piezoelectric transducers. Examples of such piezoelectric transducers are disclosed in U.S. Pat. Nos. 3,792,204; 4,793,825; 3,894,198; 3,798,473, and 4,600,855.
However, none of the prior art references provides a miniature flexural piezoelectric transducer specifically tailored so as to allow the usage of low frequency acoustic signals for vibrating the piezoelectric layer at its resonant frequency, wherein substantially low frequency signals herein refer to signals having a wavelength that is much larger than the dimensions of the transducer. Further, none of the prior art references provides a miniature transducer having electrodes specifically shaped so as to maximize the electrical output of the transducer. Further, none of the above references provides a transducer clement which may be integrally manufactured with any combination of electronic circuits by using photolithographic and microelectronics technologies
Further, the prior art fails to provide a miniature flexural piezoelectric transmitter which modulates the reflected acoustic wave by controllably changing the mechanical impedance of the piezoelectric layer according to a message signal received from an electronic component such as a sensor. Further, the prior art fails to provide such transmitter wherein the piezoelectric layer is electrically connected to a switching element, the switching element for alternately changing the electrical connections of the transmitter so as to alternately chance the mechanical impedance of the piezoelectric layer. Further, the prior art fails to provide such transducer wherein the mechanical impedance of the piezoelectric layer is controlled by providing a plurality of electrodes attached thereto, the electrodes being electrically interconnected in parallel and anti-parallel electrical connections. Further, the prior art fails to provide such transmitter wherein the piezoelectric layer features different polarities at distinct portions thereof. Further, the prior art fails to provide such transmitter which includes a chamber containing a low pressure gas for enabling asymmetrical fluctuations of the piezoelectric layer. Further, the prior art fails to provide such transmitter having two-ply piezoelectric layer.